1. Field of the Invention
This invention relates to a display device such as a direct-projection type of television receiver, a projection type display device, an image output device for a computer, etc., which utilizes a cathode-ray-tube (CRT), a liquid crystal device, a plasma device, an electroluminescence device, an electrochromic device or the like. Also, this invention relates to a method for displaying an image.
2. Description of the Prior Art
When a color image is displayed with plural dots in a conventional display device, plural colored areas such as A-colored area, B-colored area, C-colored area, D-colored area, etc., are separately displayed for any color image. Also, in both cases of monochromatic image and color image, the image is displayed with areas having different brightness being separated respectively. In this display manner, a mixing color frequently occurs at a boundary between the different colored areas on the display device, and thus a clear image can not be displayed. Also, color becomes ambiguous at a boundary between the areas having different brightness. This is not only because of the problem of the ability of the display device, but also because high frequency components in the image signal are cut when the image signal is created or processed to send the image signal to the display device, that is, before the image signal is received by the display device. The signal waveform becomes gentle by the cut. This becomes a problem particularly in the case of the display for office automation which requires high definition.
In order to overcome the above disadvantage, the following method has been adopted.
That is, as shown in FIG. 3, an original image data 1 is subjected to a profiling processing to obtain a profile image data 2, and then the original image data 1 and the profile image data 2 are synthesized with each other to obtain a synthesized image data 3, thereby displaying the synthesized image data 3 on the display device.
However, this method requires a very high-speed calculation per frame, and thus has been unsuitable for a dynamical image displaying operation which requires a displaying speed above 60 frames per second.
It is an object of the present invention to provide novel methods for displaying an image with a clear outline (profile).
It is another object of the present invention to provide an electro-optical device capable of displaying an image with a clear outline (profile).
According to one of the novel methods, the most marginal profile of neighboring same color areas is colored with black, thereby depressing the color mixing between neighboring different color areas.
In accordance with the present invention, an electro-optical device for displaying a color image with a dot matrix comprising dots on plural X-axes and Y-axes in a dot-sequential scanning operation or a line-sequential scanning operation, includes means for converting color data of most marginal positions of plural adjacent image data of same color on the X-axes into a back-color data when the image data of same color are adjacently arranged on any one of the X-axes.
According to the same concept, color data of most marginal positions of plural adjacent image data of same color on the Y-axes can be converted into a black-color data when the image data of same color are adjacently arranged on any one of the Y-axes.
According to the electro-optical device thus constructed, such a clear image (data 3) as shown in FIG. 3 can be obtained without a high-speed displaying operation utilized in the conventional display device.
In the foregoing description, when plural image data of same color are adjacently arranged, the color data at the most marginal positions of the image data are converted into back-color data to obtain a clear image. In place of the color conversion, when plural image data of same luminance (light intensity) are adjacently arranged in a gradation displaying operation, the luminance (light intensity) data at the most marginal positions of the image data may be changed to high or low luminance (great or weak light intensity) data to obtain a clear image. This technique is applied to a case where when a high-luminance image (more retina-stimulating image) is displayed with a background of low luminance, a profile of the high-luminance image (that is, a more recognizable image) is further stressed (that is, the light intensity of the profile of the image is further intensified) to thereby bring an image to be displayed (e.g., a white letter) into relief from a background (e.g., a white background) and obtain a clear image.
Therefore, in this invention, not only color-conversion to back color, but also variation of luminance (light intensity) can be performed individually or in combination when plural same color image data are adjacently arranged on the display device.
In a combination of special colors, there is a case where colors other than black color are required as the color into which the color data of the most marginal positions of the adjacently-arranged image data should be converted. This invention is also applicable to this case by changing the color conversion to the black color to the color conversion to another color.
Methods obtained by generalizing a bit mathematically the above idea are as follows.
One method is to calculate an average brightness of input image data in a specific section and then to divide the specific section into areas having brightness of input image data not lower than the average brightness and areas having brightness of input image data not higher than the average brightness. And a maximal value (maximum value) and a minimal value (minimum value) of the areas are used as output data for displaying those areas. The discontinuous maximal and minimal values of those areas may be outputted, however, tone and brightness are steeply changed between the areas in this case, so that the image thus displayed might give an unnatural impression visually. This unnaturalness can be avoided by providing a transition section between the area of the maximal value and the area of the minimal value to connect the area of the maximal value to the area of the minimal value and vice versa by new data of the transition section which are continuously changed in the brightness thereof. For example, the gradient of input image data at a cross point of input image data with the average is calculated and then a straight line having the gradient and passing through the cross point is used as the image data for the transition section.
Another method is to calculate absolute values of a derived function of the input image data and to use, as output image data for a section sandwiched between addresses having absolute values showing peaks in the derived function, the input image data at the lowest absolute values in the same section in the derived function. In this case too, discontinuous brightness is displayed as in the above method, so that the problem as mentioned above can be overcome in the same way.
Further, another method is to calculate absolute values of a derived function of the input image data and to use, as output image data, data obtained by emphasizing only the adjacency of the absolute values showing peaks. That is, since tone and brightness of the image are transiting at the peak points of the absolute values of the derived function, the presence of the transition section can be emphasized by emphasizing the adjacency of the peak points.
The above methods are effective for emphasizing the boundary between adjacent areas having different tone and brightness. That is, in the above methods, the display device has a system to distinguish boundaries and to correct images in accordance with the boundaries by some mechanical or automatic means. The display device having such a system is effective not only as a usual office automation instruments but also as a display device for amusement.
For example, 525 scanning lines are used for TV broadcasting of NTSC system. When the width of the image plane is made 1.5 times as long as the height thereof to increase the horizontal resolution to 800 lines, which is 525 lines xc3x971.5, a wideband carrier wave of at least 30 MHz is required. However, only a few MHz was applied actually, so that it was impossible to transmit fine images. In particular, the image in the width direction became blurry or ambiguous though that in the height direction had high definition. This is because high frequency components of the image carrier wave band were cut, that is, image signals were made gentle.
On the other hand, the ambiguousness of images has not been recognized in the case of CRT system. Since the CRT system utilizes dot sequential scanning system, special high frequency circuit for processing signals, e.g. electron beam having such a high frequency as 30 MHz, is indispensable.
However, conditions are different in displays such as LCD and PDP which utilize line sequential scanning system. For example, in the devices such as LCD and PDP in 800xc3x97525 matrix as the above, image signals per column are processed parallel, so that the process time is 800 times as short as that of CRT system display. Hence, the above-mentioned image processing is considered to be suitable to, specifically, LCD and PDP.